It’s Solar Power Tower Time!

There are many ways to harvest solar energy; almost all rely upon reflecting mirrors to concentrate the sunlight. The Solar Power Tower at Sandia Labs in Albuquerque utilizes a field of 218 heliostats to focus an incredible amount of concentrated sunlight onto a central point (the tower shown in the photo at left). When all of the heliostats are focused on the tower the beam produces a whopping 4000 “suns” of concentrated solar energy. Experiments can be designed to utilize this concentrated sunlight for a variety of purposes.

The day started with a tour of the solar tower, a enormous structure more than 160 feet tall. The tower has several test bays starting at 120 feet, where today’s experiment was setup and can be seen in some of the photos in the slideshow below. The tower has several calibration areas; these are water cooled regions where the solar flux can be measured prior to moving the heliostat beams onto the target. Even the roof has test areas and had frequently been used for NASA experiments.

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The Experiment

The experiment deals with characterization of a solar jet engine design. The idea is that in lieu of combusting a fuel to generate a stream of high temperature, high pressure gas, you can use concentrated solar energy to accomplish the same task. The superheated air can then be used to generate electricity. The test began with successive heliostats being brought “on target” and internal measurements where recorded. My role in the experiment involved infrared measurements from the field using an IR camera that “sees” IR emissions within the range of 1-3.3 micrometers. Some sample images while the target was not on sun can be seen below:

Sample target can be seen in the mid-right of the IR image

IR image with test bay door closed

IR images like this are useful in determining where heat is leaking or building up within a test target or material. However, the images can be misleading as an intense red color in the images above does not equate to an intense red color when the target is on sun unless the emissivity of the materials is very similar. This is apparent in the first IR image above. In this image the entire test bay had not been put on sun yet, but you can see severe variation in IR intensities due to the differing emissivities of the materials.

So the day went on and I took many IR images as the heliostat field was brought to 20%, then 40% and working up to 80% at the end of the solar window for the day (around 3:15 PDT). Experiments need to be completed within +/- 2 hours of solar noon, which was around 1pm today.